Conventional fiber optic cables comprise optical fibers which transmit information in the form of light waves. Such cables are used to transmit telephone, cable television, and data. A conventional fiber optic cable can include buffer tubes with optical fibers therein. During a cable manufacturing process, the buffer tubes may be stranded about a central member in alternating (S-Z) lay directions. More specifically, the buffer tubes are typically stranded in a first lay direction, the lay direction is then reversed, and the buffer tubes are then stranded in a second lay direction. Each location along the tubes at which the lay direction is reversed can be termed a reversal area.
Reversal area identification can assist craftsmen in fiber connection/splicing procedures. For example, in the S-Z stranded cable disclosed in U.S. Pat. No. 4,828,352,incorporated by reference herein, the buffer tube length, or tightly buffered fiber length, is advantageously longer than the length of the cable, thereby making slack available in the optical fibers at the reversal areas of the stranding. If a craftsman removes the sheath at the reversal area, the buffer tube or tightly buffered fibers there are not constrained by any unidirectional configuration. The use of a reversal mark or marks, as disclosed in U.S. Pat. No. 4,828,352, permits a craftsman to know where the excess fiber is available for ease in making fiber connections/splicing other than at the cable ends.
Automatic reversal area tracking systems have been developed for precise reversal area identification. U.S. Pat. No. 5,729,966, incorporated by reference herein, discloses a cable manufacturing process whereby reversal area marks are formed on an outer cable jacket. An optical scan detector is used to sense the location of reversal area marks made on core binders or tubes. A computer tracks the locations of the reversal areas as the cable moves along a pass-line. After extrusion of a cable jacket over the core, and when any reversal area reaches a controlled print station, the computer activates the print station and a mark is made on the cable jacket indicating the location of the reversal area.
Conventional reversal area marking techniques suggest that the marks need not be made precisely over a reversal area. For example, U.S. Pat. No. 5,809,194 discloses a cable manufacturing process for marking reversal areas or areas offset from the reversal areas. The markings are made directly on buffer tubes or a slotted core member, and are detectable by a luminescence scanner. After extrusion of the cable jacket over the tubes or slotted core, when the reversal area reaches an ink jet printer, a computer may activate the ink jet printer for marking the cable.
Camera systems requiring an interface with a memory function can be used to directly detect reversal areas. For example, U.S. Pat. No. 5,745,628 discloses a cable manufacturing process whereby marks are formed on only the outer jacket for indicating the locations of reversal areas. No marks are made within the outer jacket. Rather, a vision system includes a camera and a computer that directly views tubes and stores a threshold image of the tubes in memory and sequentially compares ongoing images of the cable core with the threshold image. When the threshold image is matched with an ongoing image, the vision system recognizes a reversal of the tubes. After extrusion of a cable jacket over the tubes or slotted core, when the reversal area reaches an ink jet printer, the computer sends a signal to the ink jet printer. The ink jet printer then marks the cable jacket.
A particular known S-Z stranded cable does not include a craft friendly mark on the cable jacket. For example, U.S. Pat. No. 5,703,983 describes marks placed between the reversal areas, but within the outer cable jacket, that indicate distances from reversal points. The marks can be made on a buffer tube core, a slotted core, a tight buffer core, a binder, a tape, or an inner jacket. The outer jacket, however, is not marked with any reversal area marking: a craftsman must therefore expend time and effort opening a window in the jacket and searching for the distance marks beneath the jacket and between reversal areas.